1. Field of the Invention
The present invention relates to an ink jet recording apparatus in which ink is discharged on a recording material for recording.
2. Description of the Related Art
The term xe2x80x9crecordingxe2x80x9d described in the present invention does not only refer to the transfer of a significant image such as a character or a figure to a recording material but also to the transfer of a non-significant image such as a pattern.
Techniques in accordance with the present invention are applicable to recording apparatuses such as printers, copying machines, facsimile machines having a communication system, and word-processors having a printer for recording on recording materials such as paper, string, fiber, cloth, leather, metal, plastics, glass, wood, and ceramics, and further applicable to an industrial recording apparatus combined with various processing apparatuses.
In one conventional type of ink jet head, bubbles are formed in ink by the heat generated by applying a driving pulse to an electro-thermal converting element (recording element), and resultant ink droplets are discharged onto a recording material, this so called xe2x80x9csingle-pulse drivingxe2x80x9d, in which one droplet is discharged in accordance with one pulse as shown in FIG. 9A, has been mainstream. In single-pulse driving, however, by printing continuously with a high-duty cycle so that the temperature of the head increases resulting in an increase volume of discharged ink, there are cases in which printing quality has been degraded.
Accordingly, double-pulse driving has been developed, as disclosed in Japanese Patent Laid-Open Publication 63-42871 and Japanese Patent Laid-Open Publication 2-74351, in which the driving pulse is divided into a pre-pulse and a main pulse, as shown in FIG. 9B. By changing a pulse width and an off-time between the two pulses, the volume of discharged ink is controlled.
On the other hand, when applying a single pulse to an electro-thermal converting element (heater) to form an ink droplet into a bubble, it is generally known that a threshold pulse width xe2x80x9cTthxe2x80x9d, at which a bubble is generated on the surface of the electro-thermal converting element, decreases almost linearly with an increase in the head temperature, as shown in FIG. 6.
With so-called xe2x80x9cTth controlxe2x80x9d the width of the driving pulse is reduced in accordance with increase in the head temperature by monitoring the head temperature. When a sensor of the head temperature has poor accuracy, however, the driving pulse to discharge a necessary volume of ink misaligns resulting in an unstable discharge, or no ink discharge in the worst case. The pulse width, therefore, has to be increased more than the necessary width by adding a safety margin.
Since further increases in resolution and throughput of printers have recently been required, the number of nozzles of a recording head and discharging frequency must be further increased. Because of increased energy per unit time required for an increased number of nozzles and discharging frequency, however, the rate of increase in temperature is much more raised than ever.
In the ink jet head, when the head temperature is raised above a specific temperature, bubbles are prone to accumulate in the pathway of the head and bubbles generated once by driving the electro-thermal converting element may not be diminished causing disturbance of the charging. It is necessary, therefore, to retain the head temperature within a specific level for normal recording. Then, if the recording head temperature is raised above the specific level, while recording, the temperature is lowered by setting a pause, by reducing the printing frequency, or by reducing the printing duty, for suppressing increase in the head temperature. This, however, results in a decrease in throughput of the printer.
In order to solve the above-mentioned problems, an ink jet recording apparatus in accordance with one aspect of the present invention comprises a recording head having a recording element for jetting ink and sensing means for sensing temperature; pulse generating means which generates a pulse signal to be applied to the recording element of the recording head such that the pulse width of the pulse signal corresponds to the head temperature; and driving means for driving the recording element of the recording head by the pulse signal generated by the pulse generating means, wherein the pulse generating means is capable of generating a plurality of signal trains of pulse widths corresponding to the head temperature, and wherein the ink jet recording apparatus further comprises means for changing the signal train corresponding to correction accuracy of the output of the temperature sensing means of the recording head.
In accordance with another aspect of the present invention, an ink jet recording apparatus comprises sensing means for sensing temperature of a head; driving pulse storing means storing driving pulse waveform data in accordance with each range of the head temperature; driving pulse generating means which reads driving pulse waveform data corresponding to head temperature from the driving pulse storing means to generate a driving pulse waveform; and driving means for driving the head in accordance with the driving waveform generated by the driving pulse generating means, wherein the ink jet recording apparatus comprises a plurality of the driving pulse storing means to select desired driving pulse storing means in accordance with correction accuracy of a temperature characteristic of the sensing means for sensing head temperature.
In accordance with still another aspect of the present invention, a driving method of an ink jet recording apparatus having a recording head including a recording element for jetting ink and sensing means for sensing temperature, the driving method comprises the steps of:
generating a pulse signal to be applied to the recording element such that the pulse width of the pulse signal corresponds to head temperature; and driving the recording element of the recording head by the pulse signal,
wherein a plurality of signal trains of pulse widths are capable of being generated in accordance with head temperature for selection of the train in accordance with correction accuracy of an output of the sensing means for sensing head temperature.
In the present invention, the head driving energy can be restrained with a corresponding to improvement in correction accuracy of the head temperature sensor by determining a relation between the head temperature and the driving pulse waveform (a table) corresponding to correction accuracy of the head temperature sensor. This may result in suppression of increase in the head temperature and restraint of degradation of throughput when recording at high duty.